3 files changed, 60 insertions, 52 deletions

diff --git a/crates/base_db/src/lib.rs b/crates/base_db/src/lib.rs
index c72e254f4..030b96829 100644
--- a/crates/base_db/src/lib.rs
+++ b/crates/base_db/src/lib.rs
@@ -167,29 +167,7 @@ impl<T: SourceDatabaseExt> FileLoader for FileLoaderDelegate<&'_ T> {
     }
 
     fn possible_sudmobule_names(&self, module_file: FileId) -> Vec<String> {
-        let module_files = &self.source_root(module_file).file_set;
-        let possible_submodule_files = match module_files.file_name_and_extension(module_file) {
-            Some(("mod", Some("rs"))) | Some(("lib", Some("rs"))) => {
-                module_files.list_files_with_extensions(module_file, None)
-            }
-            // TODO kb for `src/bin/foo.rs`, we need to check for modules in `src/bin/`
-            Some((directory_with_module_name, Some("rs"))) => module_files
-                .list_files_with_extensions(
-                    module_file,
-                    Some(&format!("../{}/", directory_with_module_name)),
-                ),
-            // TODO kb also consider the case when there's no `../module_name.rs`, but `../module_name/mod.rs`
-            _ => Vec::new(),
-        };
-
-        possible_submodule_files
-            .into_iter()
-            .filter(|(_, extension)| extension == &Some("rs"))
-            .filter(|(file_name, _)| file_name != &"mod")
-            .filter(|(file_name, _)| file_name != &"lib")
-            .filter(|(file_name, _)| file_name != &"main")
-            .map(|(file_name, _)| file_name.to_owned())
-            .collect()
+        self.source_root(module_file).file_set.possible_sudmobule_names(module_file)
     }
 }
 
diff --git a/crates/ide/src/completion/completion_context.rs b/crates/ide/src/completion/completion_context.rs
index 74cd16e0a..a8fe44083 100644
--- a/crates/ide/src/completion/completion_context.rs
+++ b/crates/ide/src/completion/completion_context.rs
@@ -1,7 +1,7 @@
 //! FIXME: write short doc here
 
 use base_db::{FileLoader, SourceDatabase};
-use hir::{ModuleSource, Semantics, SemanticsScope, Type};
+use hir::{Semantics, SemanticsScope, Type};
 use ide_db::RootDatabase;
 use syntax::{
     algo::{find_covering_element, find_node_at_offset},
@@ -123,11 +123,9 @@ impl<'a> CompletionContext<'a> {
                     dbg!(mod_declaration_candidates);
                     // TODO kb exlude existing children from the candidates
                     let existing_children = current_module.children(db).collect::<Vec<_>>();
-                    dbg!(existing_children);
                     None::<Vec<String>>
                 })
                 .unwrap_or_default();
-            dbg!(module_names_for_import);
         };
 
         let krate = sema.to_module_def(position.file_id).map(|m| m.krate());
diff --git a/crates/vfs/src/file_set.rs b/crates/vfs/src/file_set.rs
index 3085fd818..cb65c17e0 100644
--- a/crates/vfs/src/file_set.rs
+++ b/crates/vfs/src/file_set.rs
@@ -26,38 +26,70 @@ impl FileSet {
         self.files.get(&path).copied()
     }
 
-    pub fn file_name_and_extension(&self, file: FileId) -> Option<(&str, Option<&str>)> {
-        self.paths[&file].file_name_and_extension()
-    }
-
-    pub fn list_files_with_extensions(
-        &self,
-        anchor: FileId,
-        anchor_relative_path: Option<&str>,
-    ) -> Vec<(&str, Option<&str>)> {
-        let anchor_directory = {
-            let path = self.paths[&anchor].clone();
-            match anchor_relative_path {
-                Some(anchor_relative_path) => path.join(anchor_relative_path),
-                None => path.parent(),
-            }
+    pub fn possible_sudmobule_names(&self, module_file: FileId) -> Vec<String> {
+        let directory_to_look_for_submodules = match self.get_directory_with_submodules(module_file)
+        {
+            Some(directory) => directory,
+            None => return Vec::new(),
         };
-
-        if let Some(anchor_directory) = anchor_directory {
-            self.paths
-                .iter()
-                .filter_map(|(_, path)| {
-                    if path.parent()? == anchor_directory {
-                        path.file_name_and_extension()
+        self.paths
+            .iter()
+            .filter_map(|(_, path)| {
+                if path.parent()? == directory_to_look_for_submodules {
+                    path.file_name_and_extension()
+                } else {
+                    None
+                }
+            })
+            .filter_map(|file_name_and_extension| match file_name_and_extension {
+                // TODO kb do not include the module file name itself, if present
+                // TODO kb wrong resolution for nesСпаted non-file modules (mod tests {mod <|>)
+                // TODO kb in src/bin when a module is included into another,
+                // the included file gets "moved" into a directory below and now cannot add any other modules
+                ("mod", Some("rs")) | ("lib", Some("rs")) | ("main", Some("rs")) => None,
+                (file_name, Some("rs")) => Some(file_name.to_owned()),
+                (subdirectory_name, None) => {
+                    let mod_rs_path =
+                        directory_to_look_for_submodules.join(subdirectory_name)?.join("mod.rs")?;
+                    if self.files.contains_key(&mod_rs_path) {
+                        Some(subdirectory_name.to_owned())
                     } else {
                         None
                     }
-                })
-                .collect()
-        } else {
-            Vec::new()
+                }
+                _ => None,
+            })
+            .collect()
+    }
+
+    fn get_directory_with_submodules(&self, module_file: FileId) -> Option<VfsPath> {
+        let module_file_path = &self.paths[&module_file];
+        let module_directory_path = module_file_path.parent()?;
+        match module_file_path.file_name_and_extension() {
+            Some(("mod", Some("rs"))) | Some(("lib", Some("rs"))) | Some(("main", Some("rs"))) => {
+                Some(module_directory_path)
+            }
+            Some((regular_rust_file_name, Some("rs"))) => {
+                if matches!(
+                    (
+                        module_directory_path
+                            .parent()
+                            .as_ref()
+                            .and_then(|path| path.file_name_and_extension()),
+                        module_directory_path.file_name_and_extension(),
+                    ),
+                    (Some(("src", None)), Some(("bin", None)))
+                ) {
+                    // files in /src/bin/ can import each other directly
+                    Some(module_directory_path)
+                } else {
+                    module_directory_path.join(regular_rust_file_name)
+                }
+            }
+            _ => None,
         }
     }
+
     pub fn insert(&mut self, file_id: FileId, path: VfsPath) {
         self.files.insert(path.clone(), file_id);
         self.paths.insert(file_id, path);